1. Field of the Invention
The present invention relates to an apparatus and a method for detecting a femto Base Station (BS) in a wireless communication system. More particularly, the present invention relates to an apparatus and a method for detecting a neighbor femto BS of a Mobile Station (MS) through UpLink (UL) monitoring of the femto BS with respect to the MS in a wireless communication system including a macro BS and a femto BS.
2. Description of the Related Art
In current high rate mobile communications, many wireless communication technologies are suggested as candidates. Among the wireless communication technologies, an Orthogonal Frequency Division Multiplexing (OFDM) technology is acknowledged as the most dominant next-generation wireless communication technology. In the future, it is expected that the OFDM technology will be used in most of the wireless communications. Wireless Metropolitan Area Network (WMAN) of the Institute of Electrical and Electronics Engineers (IEEE) standard 802.16 called 3.5-generation technology is adopting the OFDM technology as its standard.
The OFDM scheme transmits data using a multi-carrier. The OFDM scheme is one of a Multi Carrier Modulation (MCM) scheme which converts an input serial symbol stream in parallel, modulates the input serial symbol stream to orthogonal subcarriers, that is, to subchannels, and then transmits the subchannels.
In a cellular wireless communication system, when channel status is deteriorated because of a geographical condition in a cell, a distance between a Mobile Station (MS) and a Base Station (BS), or movement of the MS, the MS and the BS may not normally communicate with each other. For example, even in a service coverage of the BS, a building such as an office or a house forms a shadow zone. When the MS travels in the shadow zone, the BS cannot normally communicate with the MS because of a poor channel status with the MS.
In this respect, the wireless communication system provides a femto-cell service to address the service problem in the shadow zone and to offer a high-rate data service. The femto-cell is a small cell formed by a compact BS, which is installed indoors such as in an office or in a house, to connect to a mobile communication core network over a broadband network. The compact BS, which is a low-power BS installed by a user, can also be called a micro BS, a self-configurable BS, an indoor BS, a home BS, and a femto BS. Hereinafter, the compact BS is referred to as the femto BS.
Meanwhile, when the MS transits from a serving BS which services the MS to a coverage of another neighbor BS, the MS hands over for providing continuous service. Accordingly, it is necessary to select a handover target BS. The IEEE standard 802.16e system considers a scheme in which the MS receives a neighbor BS list from its serving BS through broadcast information and selects the handover target BS by searching neighbor BSs using the neighbor BS list. A 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system deliberates on a scheme in which the MS selects the handover target BS by scanning an entire preamble without a separate neighbor BS list.
When a macro BS and a femto BS coexist, a number of the BSs per unit area can abruptly increase, compared to an area including only macro BSs. When the macro BS broadcasts the neighbor BS list with respect to every femto BS in the macro cell to provide information of the neighbor femto BSs to the MS, excessive waste of radio resources is resulted. However, when the neighbor BS list of the neighbor femto BSs is not provided to the MS, the MS needs to detect the neighbor femto BS by scanning every preamble in every Frequency Allocation (FA). This process requires a lot of computation and a considerable amount of time scanning. Due to a delay of data transmission during the scanning of every preamble in every FA, a real-time service is difficult to provide.
Thus, a need exists for an apparatus and method for minimizing unnecessary scanning when an MS scans to detect a neighbor femto BS in a wireless communication system.